Manufacturing method for electrical contacts



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' usw-Acronis Immo ion' x=.'x.xmrca1.` conuc'rs Inventor; Benjamin E., Spiro,

Patented Apr. 22, 1947 MANUFACTURING METHOD FOR ELECTRICAL CONTACTS,4v

Benjamin E. Spiro, Philadelphia, Pay.; assignor to General Electric Company, a corporation of New York Application April 24, 1943, Serial No. 484,361

of a material different from the main conducting parts of the electrical apparatus For example, the current carrying contacts of electric switches such as circuit breakers or relays are often provided with contact surfaces formed of a material the'oxide of which does not substantially inter- 1ere with electrical current conduction. The conducting parts of switches are usually made from copper, but since copper oxide substantially interferes with electrical current conduction, it has become good practice to provide the contacting surfaces of such conducting parts with a coating of silver or the like the oxide of which is both physically and chemically unstable so as not to substantially interfere with electric current conduction.

Again, contacts whose contact surfaces are subject to arcing in electric circuit breakers are often provided with a local contact surface which is capable of withstanding extreme heat without deleterious effects therefrom such as pitting or burning. For this type of dutyit is advantageous to provide a contact surface formed of a sintered and impregnated tungsten material of the type such as is disclosed, for example, in U. S. Patent 1.552,184 and which is sold under the trade-mark Elkonite. This and other comparable arc-resisting materials are well known in the electrical art. My invention is particularly concerned with a new and improved method of constructing contacts of the above-mentioned type in which a contact surface is formed of a material different from the material from which the main body of the contact element is constructed.

It is an object of my invention, therefore, to provide a new and improved manufacturing method `for applying a contact surface at the engaging part of a current conducting member for electrical apparatus.

It is another object of my invention to provide a new and improved method of producing a contacting surface of the engaging part of a current conducting member for electrical apparatus, the contacting surface being of silver and the conducting member being of copper.

Further objects and advantages of my invention will become apparentA as the following description proceeds and the features of novelty which characterize my invention will bepointed out with particularity in the claims annexed to and forming a part of this application.

Fora better understanding of my invention, reference may be had to the accompanying drawing in which Fig. 1 is a diagrammatic representation of an electrical apparatus employing a contact produced in accordance with the teaching of my invention, Figs. 2 and 3 represent stages during the process of constructing the contact surface of my invention. Fig. 1l is similar to Fig. 3 representing a modified step in the construction of the contact surface oi' my invention, .and Fig.

- 5 is a perspective view of afanged plug used in producing the new and improved contact surface of my invention.

Although my invention vmay be applied generally in connection with the contact surfaces of electric switches and relays, I have chosen to specifically illustrate my invention in connection with the current carrying contact vof an electric circuit breaker.

Referring now to Fig. 1 of the drawing, I have shown a circuit breaker i0 of the well-known drop-down type for use in a grounded metal .enclosure or cubicle not shown, wherein discon- 'V nection from anexternal electric circuit is effected merely by bodily lowering of the circuit breaker. Circuit breaker it includes a movable contact structure including a pair of relatively movable current carrying contacts li and l2.

vMy invention is concerned with the current carrying contact il and particularly the method of producing the same. Contact i i is really a contact iinger shown in enlarged View in Figs. 2, 3 and 4. Contact fingers similar in shape to contact finger il of Fig. l have been used extensively in switch-gear of the type disclosed as, for example, in United States Letters Patent 2,293,513, granted August 18, 1943, upon an application of Leonard J. Linde and assigned to the same assignee as the present application.

Various means of constructing these contact .fingers have been employed and the contacting 'surface generally indicated at Il in Fig. 1, has' comprised a piece of silver, for example, which has been bonded to the conducting members as by welding, soldering or by the cementation processes disclosed and claimed in United States Letters Patent 2,094,482vand 2,094,483, granted September 28, '1937, upon applications of William J. Weder and assigned to the same assignee as the present application. After many thousands of current interrupting operations, we have found that contacts constructed in accordance with my invention, show considerably less mechanical wear than contacts constructed in accordance with the teachings of the prior art.

I'he contact linger II usually constructed of an electric conducting material such as copper, is rst formed by a stamping or extruding operation so that long strips of material having a cross section of the general form shown by the tact finger adjacent recess I5, so as to assume the form indicated in Fig. 2. The contact finger II is then plated with silver or the like so that the interior of recess I5 is also plated.' Next a flanged plug I6 of a. material the oxide of which does not substantially interfere with current conduction is inserted in the circular recess I5 with the flange I'I at the bottom of the recess as indicated in Fig. 2. The flanged plug I6, best shown in Fig. 5, lmay be silver if, for example, a current carrying contact is to be produced, or may be of the already identified heat-resistant material Elkonite if an arcing contact is to be produced. Flanged plug I6 is generally in'the form of a button having an integral/enlargement I1 and as mentioned raloeyes"positioned in the recess ls with said/miargement n at the bottom of the recess.

The completed contactlsurface II' is obtained as indicated in Fig. 3, by means of-a cold upsetting punch press operation with a smooth radius tool such as is indicated at I8, whereby a hard' planlshed surface II is obtained which produces a very satisfactory contact. The silver plating in'the recess I5 and the silver flanged plug I8 unite into a silver-to-silver bond so as to form a good current carrying contact. Furthermore, the edges of the recess are clinched over as indicated at I9 to engage the enlargement or flange I1 of the button or flanged plus I6, thereby holding the flanged plug as if it were an integral part of the contact finger I I.

The tool I 8 of Fig. -3 provides a uniformly rounded contact surface which is very suitable for a current carrying contact. In the event that it is desired to produce an arcing contact having a contact tip such as Elkonite, it might be desired to have the contact tip of the arcing material extend above the surface of the material from which contact finger Il is constructed. Such an arrangement is disclosed inv Fig. 4

in which the upsetting tool I8 is shaped so as to permit the surface II' to extend above the surrounding portions of the contact finger II to provide an arcing tip. If a contacting surface is constructed such as is illustrated in Fig. 4, the contacting -material projecting above the surface of the contact finger is available for filing or dressing in the event it becomes pitted or otherwise damaged, and which dressing operation is not possible with the construction illustrated in Fig. 3 without affecting the surrounding silver-plated portion of the contact finger I I.

From the above discussion, it will be obvious that a new and `improved contact construction is provided which is much simpler to manufacture, in that it permits of a considerable saving oi! labor and, in additionrequiresV a smaller percentage of the silver or other material for the contact surface than is required by the prior art arrangements. Also the cold upsetting operation does not produce any annealing of the contact material so that better wearing qualities are obtained.

While I have disclosed certain specic methods of carrying out the contact producing process of my invention, it should be understood that my invention is not limited to the specic details and methods of construction thereof herein illustrated, and I intend in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. The method of producing a contact surface from a material whose oxide does not substantially interfere with current conduction on a switching mem-ber which comprises, forming a circular recess in said member, plating said member with silver, placing a button having an integral enlargement at one end into said recess with said enlargement at the bottom of said recess and with the other end of said button substantially ilush with the edges of said circular recess, and bonding said button to said member by clinching the edges of said recess over said enlargement by a cold upsetting operation so that said other end of said button forms the contacting portion of said contact surface.

2. The method of producing a contact surface of silver on a switching member of copper which comprises, forming a circular recess in said member, plating said member including said recess with silver, placing a silver button having an integral enlargement at one end into' said recess with said enlargement at the bottom of said recess and with the other end of said button substantially flush with the edges of said recess, and bonding said button to said member by clinching the edges of said recess ,over said enlargement by a cold upsetting operation while simultaneously producing a silver-to-silver bond between said button and the plated surface of said recess.

3. The method of producing a silver contact surface on a copper switching member which comprises forming a circular recess in said member. plating said member with silver, placing a flanged plug of silver in said recess with the flange thereof at the bottom of said recess and the unilanged end thereof substantially ush with the edges of said circular recess, and bonding said ilanged plug to said member by clinching the edges 'of said recess over said flange Iby a cold upsetting operation.

^ BENJAMIN E. SPIRO.

REFERECES crrED The following references are oi record in the le of this patent:

UNITED STATES PATENTS Number Name Date 953,306 Taylor Mar. 29, 1910 2,137,617 Jones Nov. 22, 193B Re. 17,108 Brown --5 Oct. 23, 1928 2,013,411 Hummell Sept. 3, 1935 2,117,353 Park May 17, 1938 1,837,238 Siegmund Dec. 22, 1931 

